perf: Make the trace events sample period default to 1

Trace events are mostly used for tracing and then require not to
be lost when possible. As opposite to hardware events that really
require to trigger after a given sample period, trace events mostly
need to trigger everytime.

It is a frustrating experience to trace with perf and realize we
lost a lot of events because we forgot the "-c 1" option.

Then default sample_period to 1 for trace events but let the user
override it.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 22 insertions, 14 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index dcda8993082d..ca2affc9233f 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -33,11 +33,13 @@ enum write_mode_t {
 
 static int                      *fd[MAX_NR_CPUS][MAX_COUNTERS];
 
+static unsigned int             user_interval                   = UINT_MAX;
 static long                     default_interval                =      0;
 
 static int                      nr_cpus                         =      0;
 static unsigned int             page_size;
 static unsigned int             mmap_pages                      =    128;
+static unsigned int             user_freq                       = UINT_MAX;
 static int                      freq                            =   1000;
 static int                      output;
 static const char               *output_name                    = "perf.data";
@@ -255,10 +257,19 @@ static void create_counter(int counter, int cpu)
         if (nr_counters > 1)
                 attr->sample_type |= PERF_SAMPLE_ID;
 
-        if (freq) {
-                attr->sample_type       |= PERF_SAMPLE_PERIOD;
-                attr->freq              = 1;
-                attr->sample_freq       = freq;
+        /*
+         * We default some events to a 1 default interval. But keep
+         * it a weak assumption overridable by the user.
+         */
+        if (!attr->sample_period || (user_freq != UINT_MAX &&
+                                     user_interval != UINT_MAX)) {
+                if (freq) {
+                        attr->sample_type       |= PERF_SAMPLE_PERIOD;
+                        attr->freq              = 1;
+                        attr->sample_freq       = freq;
+                } else {
+                        attr->sample_period = default_interval;
+                }
         }
 
         if (no_samples)
@@ -689,13 +700,13 @@ static const struct option options[] = {
                             "CPU to profile on"),
         OPT_BOOLEAN('f', "force", &force,
                         "overwrite existing data file (deprecated)"),
-        OPT_LONG('c', "count", &default_interval,
+        OPT_LONG('c', "count", &user_interval,
                     "event period to sample"),
         OPT_STRING('o', "output", &output_name, "file",
                     "output file name"),
         OPT_BOOLEAN('i', "inherit", &inherit,
                     "child tasks inherit counters"),
-        OPT_INTEGER('F', "freq", &freq,
+        OPT_INTEGER('F', "freq", &user_freq,
                     "profile at this frequency"),
         OPT_INTEGER('m', "mmap-pages", &mmap_pages,
                     "number of mmap data pages"),
@@ -716,7 +727,6 @@ static const struct option options[] = {
 
 int cmd_record(int argc, const char **argv, const char *prefix __used)
 {
-        int counter;
         int i,j;
 
         argc = parse_options(argc, argv, options, record_usage,
@@ -774,6 +784,11 @@ int cmd_record(int argc, const char **argv, const char *prefix __used)
         if (!event_array)
                 return -ENOMEM;
 
+        if (user_interval != UINT_MAX)
+                default_interval = user_interval;
+        if (user_freq != UINT_MAX)
+                freq = user_freq;
+
         /*
          * User specified count overrides default frequency.
          */
@@ -786,12 +801,5 @@ int cmd_record(int argc, const char **argv, const char *prefix __used)
                 exit(EXIT_FAILURE);
         }
 
-        for (counter = 0; counter < nr_counters; counter++) {
-                if (attrs[counter].sample_period)
-                        continue;
-
-                attrs[counter].sample_period = default_interval;
-        }
-
         return __cmd_record(argc, argv);
 }